Project Summary The goal of this proposal is to assess the bone repair potential of human bone marrow cells transduced with a lentiviral vector containing the cDNA for BMP-2. There are a number of difficult bone repair scenarios for which there is no consistently satisfactory solution including: fracture nonunion, acute fractures with extensive bone loss, revision total joint arthroplasty and pseudarthrosis of the spine. Traditionally, autologous bone graft has been the gold standard but there is a limited supply of this bone and there are concerns regarding the morbidity associated with graft harvest. Recombinant bone morphogenetic proteins (BMP) are FDA approved for use in spinal fusion and treatment of fresh tibial fractures. However, BMPs have had mixed success in humans and are associated with side effects including soft tissue edema and heterotopic ossification. Orthopaedic surgeons have been searching for alternative tissue engineering strategies to enhance bone repair. Our plan is to develop regional gene therapy using transduced bone marrow cells as one aspect of a comprehensive tissue engineering strategy to enhance bone repair. It has been demonstrated in animal models that gene therapy with BMP producing bone marrow cells created via lentiviral gene transfer has the potential to treat either medium or large bone defects or when the biological environment of the host is severely compromised. In this proposal we plan to test our hypothesis that human bone marrow cells transduced with a lentiviral vector to overexpress BMP-2 have the potential to enhance bone repair in humans. Human bone marrow cells will be harvested from the intramedullary canals of patients undergoing total hip arthroplasty. The cells will be transduced with a lentiviral vector (LV-TSTA-iC9/BMP-2) that contains the cDNA for BMP-2 and an inducible suicide gene (iCaspase 9) and then implanted in a critical sized femoral defect model in nude rats. We propose the following aims to accomplish the goal including: 1) compare the efficacy of regional gene therapy after bone repair with freshly isolated or cultured expanded human bone marrow cells; 2) establish a ?cellular dose? of transduced cells that can be scaled up for use in humans; and 3) determine the local and systemic biodistribution of BMP transduced human cells and assess for organ toxicity, vector genotoxicity and heterotopic ossification. The data obtained from this proposal will provide critical information with respect to adapting this regional gene therapy strategy as a treatment regimen in humans.